Filter media for tetratec ex range and other external filtersr highly active biological filtration large surface area 62cm2 per ball for growth of beneficial bacteriar excellent water flow through balls prevents clogging and dead areas for maximum biological efficiency easy to clean with aquarium waterr rinse in lukewarm water before user suitable for all external filtersr 800ml 1 pack is sufficient for the tetratec ex 600 amp ex 700r 2 packs are sufficient for the tetratec ex 1200